Optical brightening



United States Patent 3,137,655 OPTICAL BRIGHTENlNG i i Horst Taul,Obernburg (Main), and Erwin Summer,

Wuppertal Elberfeld, Germany, assignors to VereinigteGlanzstofi-Fabrilren AG., Wuppertal- Elberfeld, Germany No Drawing.Filed Mar. 21, 1961, Ser. No. 97,131 5 Claims. (Ci. 252-3ii1.2)

This invention relates to the optical brightening of polyamide textiles,and in particular to the use of a novel brightening agent havingimproved properties of wash fastness and light fastness whenincorporated in polyamides.

' It is known that synthetic linear polyamides such as nylon andpolycaprolactam become yellow as they age, and this quality isespecially noticeable and undesirable in textile materials which arewhite rather than colored. In order to avoid or reduce this yellowing,it has been a common practice to incorporate so-called opticalbrightening agents in the polyamide textile material, particularly thosebrightening or whitening agents which give a more or less intense bluefluorescence, thereby masking the yellow color of the polyamide. Manycompounds have been employed for this purpose, and the whitening orbrightening effect is often quite successful fora short.

period of time after treatment of the textile. However, where thetextile must be frequently washed, the brightening effect wears awaybecause of a poor Wash fastness of the brightening additive. Also, thelight fastness of the brightening agent is often poor because many ofthese compounds will decompose under the action of light, and thedecomposition products which adhere to the textile cause an even greaterthan normal yellowing effect. Permanent brightening efiects aretherefore quite diflicult to achieve, and it is usually necessary to addfresh agents to a textile material at frequent intervals.

One object of the present invention is to provide an optical brighteningagent for polyamide textiles which is characterized by its outstandingqualities of wash fastuess and light fastness.

Another object of the invention is to provide a method of treatingpolyamide textiles such that they will exhibit an enduring brightness inspite of repeated washing and exposure to light.

Still another object of the invention is the provision of an improvedpolyamide temile as a composition of matter containing the specialoptical brightening agent disclosed hereinafter.

Other objects and advantages will become more apparent upon aconsideration of the following detailed specification.

In accordance with the present invention, it has now been found thatpolyamide textiles can be brightened or whitened so as to obtain theabove objects by employing as the optical brightening agent the compoundof the formula:

This compound is distinguished from previously known brightening agentsby the presence of the carboxyl group in the benzimidazole derivative.It was quite surprising to find that this substitution of a carboxylgroup would lead to an improved and lasting fluorescence and brighteningeffect because there has been a prevailing opinion in this art that theuse of a carboxyl substituenhraswell as chlorine and brominesubstituent, will impair or destroy the desired fluorescence.Accordingly, the present invention isdirectly contrary to theoreticalexpectations, and no attempt will be made herein to give a scientificexplanation of the results which have been obtained. I

As polyamide textiles, the synthetic products known as nylon andpolycaprolactam are especially improved by:

the optical brightening agent of the invention. The terms textile andtextile materials are employed herein with reference to the solidpolyainide regardless of the particular form which it may require for acertain textile use. The finished article may be in the formof'filaments, fibers, yarn, thread, rope, woven 'or knitted fabrics,film, felted fibers or the like.

The brightening agent of the above formula can be readily obtained byreacting Z-methyI-benzimidazole with benzaldehyde-carboxylic acid-4 inthe molten state ac- V cording to the equation:

.denced by the solidification of the' melt. The solid product can thenbe Washed several times with cold alcohol to obtain the substantiallypure brightening agent according to this invention.

The best brightening effect is obtained if the compound of the inventionis incorporated in the polyamide by addition to the monomeric materialsfrom which the polyamide is produced, 'e.g. by polycondensation. Theaddi tion of the brightening agent prior to or during polycondensationis therefore of special technical interest. In this way, the brighteningagent is uniformly dispersed throughout the polyamide structure whichcan then be spun or extruded into various textile forms inthe usualmanner. If desired, the brightening agent can also be applied to thepolyamide textile materials as an aftertreatment, i.e. afterpolycondensation.

A good brightening or whitening eifect can be achieved by employing atleast 0.02% by weight of the brightening agent with reference to theWeight of the polyamide. Large amounts of the brightening agent arepossible but unnecessary, and the maximum amount should ordinarily notexceed about 0.5% by weight with respect to the polyamide. Optimumresults have been obtained by em- Patented June 16, 1964 3 ploying about0.1 to 0.2% by weight of the brightening agent in the finished article.

The following examples are intended solely for the purpose ofillustrating the invention in a preferred form, and the invention is notto be limited thereby. Percentages are by weight unless otherwisespecified.

Example 1 The compound of the formula:

COH=GH -COOH is added to an aqueous 95% caprolactam solution in anamount of about 0.1% (with reference to the finished polyamide). Themonomer is polymerized in the usual manner, and the resultingpolycaprolactam containing the designated brightening agent is melt-spuninto filaments. These filaments exhibit a good luminescent orbrightening effect which is not lost even after frequent washing.

Under continuous exposure to light, the filaments do not become yellowand there is no indication of decomposition of the brightening agent orloss of its luminescent effect. As regards such light fastness, thebrightening agent of the invention is superior to all known additiveswhich are commercially available at the present time.

By comparison to the compound of the formula:

(II) /N C CH=CH 1 under otherwise identical conditions, the brighteningagent of the invention provides a substantial and surprisingimprovement, both with respect to wash fastness and light fastness.

Example 2 The brightening agent of Example 1 is added in the same mannerprior to polycondensation of the caprolactam, but in an amount of 0.2%by weight with reference to the finished polyamide article. Theresulting product is likewise characterized by a very strong andenduring fastness to washing and light.

Example 3 The brightening agent of Formula I above is added tohexamethylenediamine adipate as the monomeric reactant in the productionof nylon in an amount corresponding to about 0.15% by weight withreference to the polyamide product. After polymerization, the polyamideis spun into nylon filaments by conventional melt-spinning.

These filaments can be employed as continuous or staple filament yarnsand woven or knitted to form fabrics or the like. The filaments andfabrics formed therefrom exhibit excellent light-fastness with a highstability to frequent washing.

This is a continuation-in-part application of our prior copendingapplication Serial No. 13,993, filed March 10, 1960, now abandoned.

The invention is hereby claimed as follows:'

1. A textile product comprising a polyamide selected from the groupconsisting of polycaprolactam and polyhexamethylenediamine adipamidecontaining as an optical brightening agent the compound of the formula:

ing as an optical brightening agent the compound of the formula:

References Cited in the file of this patent UNITED STATES PATENTS2,345,700 Dreyfus Apr. 4, 1944 2,349,979 Moldenhauer et a1 May 30, 19442,791,564- Fleck May 7, 1957 2,793,192 Leavitt May 21, 1957 2,965,648Wiegand et al. Dec. 20, 1960 2,985,661

Hein et al. May 23, 1961

5. A SYNTHETIC LINEAR POLYAMIDE TEXTILE ARTICLE CONTAINING AS AN OPTICALBRIGHTENING AGENT THE COMPOUND OF THE FORMULA:BENZIMIDAZOL-2-YL-CH=CH-(1,4-PHENYLENE)-COOH